Mass Spectra of Butyl Esters and N-Trifluoroacetyl Butyl Esters of Some Iminodicarboxylic Acids upon Electron Impact

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Abstract
Mass spectra (electron impact at 20 eV) of butyl esters and N-trifluoroacetyl (TFA) butyl esters of some iminodicarboxylic acids (IDCAs) were determined by gas chromatography-mass spectrometry. The IDCAs included iminodiacetic acid (1), 2-(carboxymethylamino)propionic acid (2), 3-(carboxymethylamino)propionic acid (3), 2,2′-iminodipropionic acid (4), 2,3′-iminodipropionic acid (5), 3,3′-iminodipropionic acid (6), N-methyliminodiacetic acid (7), and nitrilotriacetic acid (8). The mass spectra of the butyl ester derivatives are simple, exhibiting the corresponding molecular (M+) ions with the exception of 5. The α,α′-IDCAs (1, 2, 4, 7, and 8) are characterized by M+, M −101 (COOC4H9) (base peak), and M −157 (COOC4H9+C4H8) ions. The β,β′-IDCA (6) is characterized by a more complex spectrum with M+, M −73 (OC4H9), M −115 (CH2COOC4H9) (base peak), M −129 (OC4H9+C4H9), and M −171 (CH2COOC4H9+C4H9) ions. The α,β′-IDCAs (3 and 5) in general show spectra in which both ions characteristic of α,α′- and β,β′-IDCAs are observed. The addition of TFA to the imino nitrogens of 1–6 increases complexity of the resulting spectra. In these instances, although M+ ions are usually present, neither M −101 nor M −115 ions are base peaks. The fragmentation pathways of these two volatile derivatives of the IDCAs upon electron impact are discussed.